Inland water flows and use

2011

 

For further information, see Chapter 4: Inland water.

2.2.1 Coastal river and estuary pollution

River pollution often arises from upstream development and land use. However, it has particular impacts on the environment where it enters estuaries and the nearshore coastal environment. Some of the most significant of these estuaries and coastal lagoons are near our major cities (Sydney, Melbourne, Brisbane, Adelaide, Perth) or significant environmental assets (the Great Barrier Reef).

The land is a major source of coastal and marine pollution. Considerable progress has been made in addressing point-source pollution, although some problems still arise from these sources. Current diffuse pollution to catchments often results from historical land clearing and land-use changes. Urban stormwater is a major non–point source. Although extensive land clearing for agriculture has been considerably reduced in Australia, the legacy of sedimentation and salinisation of rivers continues. The millennium drought (lasting from 2000 to 2010 throughout southern Australia, but starting in 1997 in some areas) slowed some of these degrading processes in places, but it is likely that subsequent flooding will bring these issues back to the fore among environmental concerns.

Chapter 4: Inland water gives examples of major short-term increases in sedimentation after bushfires in south-eastern Australia (due to reduced vegetation cover and exposure of soil) and major longer term (25–30 years post-fire) reductions in water yield (due to regrowth of vegetation).

2.2.2 Desalination

Most Australians live in metropolitan areas, most of which are located on the coast. Although many of these cities draw water from inland areas, pressure is increasing for them to be able to replace or supplement these inputs by collecting the water that falls as rain in their metropolitan areas and/or by desalinating sea water, as a hedge against climate change. This would reduce further pressure on local freshwater resources. However, it entails a potential risk to coastal waters if salt is disposed of into these waters, and will increase the overall energy use in our cities.

The amount of desalination undertaken by Australian cities increased sharply during 2005–10, largely in response to drought, climate uncertainty, population increase and a new understanding of the need to provide water flows to the environment. Desalination plants were commissioned in Sydney and at Tugun in south-east Queensland in 2010; others are under construction in Melbourne (completion 2011), Perth (completion 2011) and Adelaide (completion 2013). However, desalination is not a universal strategy, as many local governments have sought to manage demand for water and improve water saving at municipal and household levels, often avoiding the need for major new water infrastructure.

2.2.3 Seawater intrusion

Development of groundwater resources to meet growing demands at the coast can put local aquifers at risk of seawater intrusion. Before development, groundwater gradients are naturally towards the sea and maintain an interface between fresh and salt water. If aquifers are exploited too heavily, this gradient can reverse and draw sea water into previously fresh aquifers. Rising sea levels also have the potential to reverse this gradient.

A number of locations around Australia have already been identified where seawater intrusion is a concern, including coastal locations in Queensland (Lower Burdekin, Bribie Island and the Pioneer Valley), South Australia (Eyre Peninsula, Port McDonnell and metropolitan Adelaide), Victoria (Port Phillip, Westernport and Werribee) and Western Australia (Swan Coastal Plain, Carnarvon, Esperance, Cottesloe and Cape Range).

Coastal development leading to increased groundwater use, potentially exacerbated by sea level rise, poses a risk to fresh groundwater resources and the people and natural environments they support.

2.2.4 Impacts of water abstraction on flora and fauna

Coastal environments and the species that inhabit them are particularly vulnerable to the effects of drought, because the impacts of drought are exacerbated by withdrawal (abstraction) of water for human use along rivers before they reach the coast. Impacts on waterbird and shorebird populations due to abstractions and extended drought were evident by 2008. The annual survey of waterbird communities at the Living Murray icon sites found a 48% decrease in bird numbers from the previous year. No waterbird breeding was recorded at the Lower Lakes, Coorong and Murray mouth, and only minimal breeding of white ibis and black swans was recorded at Chowilla Floodplain and Lindsay–Wallpolla islands. The decline of inland wetlands was identified as a significant contributor to the drastic decline in shorebirds (73% and 81% declines for migratory and resident shorebirds, respectively) between 1983 and 2006.

2.2.5 Responses

Management of coastal waters has improved greatly in Australia during the past decade, including some high-profile programs to ensure river and estuary health in metropolitan areas (e.g. Hobart and Brisbane). These programs have developed and tested cost-effective approaches to monitoring, modelling, reporting, innovation, communication, strategic interventions and effective partnerships between researchers and managers. Another successful approach to the management of coastal waters is described in Box 11.1.

Box 11.1 The Lower Lakes, Coorong and Murray mouth—Ngarrindjeri ruwe

The Lower Lakes, Coorong and Murray mouth in South Australia extend over approximately 140 000 hectares, covering 23 different wetland types, from very fresh to saltier than the sea. This area, where the Murray River meets the sea, is one of 10 major havens for large concentrations of wading birds in Australia, and is recognised internationally as a breeding ground for many species of waterbirds and native fish. The area was designated as a Ramsar Wetland of International Importance in recognition of its diverse range of wetland ecosystems, habitats and species of birds, fish and plants (more than 30% of the migratory wading birds that fly to Australia spend summer there). It is also of high cultural, economic, spiritual and social value to the Ngarrindjeri people, the traditional owners of the region, who maintain a continuous, strong relationship with their land and waters (ruwe).

Cultural flows are essential for the continued breeding and health of Ngarrindjeri ngartjis (totems), which determine the health of the Ngarrindjeri nation. Cultural flows are also essential to maintain the health of Ngarrindjeri cultural heritage sites. Some of these are areas of high cultural significance but have not been identified as being environmentally significant.

Years of water overallocation and the severe drought of 2001–10 led to significant impacts on the Coorong, Lower Lakes and Murray mouth. Due to the barrages holding back sea water, water levels in the lakes dropped to unprecedented lows—more than one metre below sea level in Lake Alexandrina in April 2009. As the water levels fell, serious land and water management issues emerged, with the drying of wetlands, exposure of previously submerged sulfidic soils and disconnection of different elements of the system. The water quality of the system declined markedly due to insufficient freshwater flows through the barrages.

The Lower Lakes, Coorong and Murray mouth icon site environmental management plan commits to protect and restore natural habitats, restore viable populations of native species, improve water quality and increase flows through the wetlands, as well as recognising the Ngarrindjeri association with the area. The short-term emergency response included the pumping of water from Lake Alexandrina to Lake Albert to prevent acidification; preparatory work towards the ponding of fresh water within the Finniss River and Currency Creek area to help manage acidification, as well as trials to assess the effectiveness of revegetation and bioremediation techniques to manage acid sulfate soils; and the purchase of water on the temporary water market to provide flows to the lakes.

Throughout the crisis, Ngarrindjeri elders worked closely with the South Australian Department of Environment and Natural Resources to put in place the emergency works and plan for the future of the Coorong, Lower Lakes and Murray mouth, and actively participated in the bioremediation and revegetation around the Lower Lakes. In recognition of their contributions, the Ngarrindjeri elders were awarded the 2010 South Australian Environment Award.

Cork S (2011). Coasts: Inland water flows and use. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/11-coasts/2-major-issues/2-2-inland-water, DOI 10.4226/94/58b659bdc758b